Indian Journal of History of Science, 51.3 (2016) 431-442 DOI: 10.16943/ijhs/2016/v51i3/48846 Mud Plaster Wall Paintings of Bhaja Caves: Composition and Performance Characteristics M Singh*, S Vinodh Kumar**and Sujata Waghmare*** (Received 30 May 2016; revised 05 August 2016) Abstract The historic mud plaster of Bhaja caves dated back to 1st century BC to 3rd century AD were investigated for their mineralogical, micro – structural and chemical characterisation. The analytical studies were performed using petrological microscope, thin section analysis, XRF, Laser particle size analyser, FTIR, XRD and scanning electron microscope. The traditional mud plaster is applied in two layers and thickness of inner layer depends on the topography of the basaltic stone surfaces. From the analytical examinations, it appears that in high rain fed regions of India’s Western Deccan, fine clayey soil (clay>65%, sand 20-28% and silt 7-15%) has been sourced for the preparation of earliest mud plaster of Bhaja caves and its properties modified by deliberate mixing of slaked lime, sand and proteinaceous adhesive to enhance cementing properties. SEM photomicrographs reveal presence of elongated kaolinitic ‘verm’ and inter wired filamentous clay ribbons of illite- sepiolite in the plaster. The shrinkage property of the plaster has also been modified by addition of rice husk as vegetal additives. The present study favours methodological approach for preparing compatible mud plaster needed for the restoration of Bhaja caves. Key words: Calcite, Clay soil, Illite-sepiolite, Kaolinite, Mud plaster 1. INTRODUCT I ON lying out and cutting the caves and not fully aware Bhaja represents the earliest cave about the problems presented by flawed basaltic architecture in Western Deccan after a century of scrap (Sundarajan, 1957-59). As technicians abandonment and decline of this artistic form. The have to struggle in the beginning during their site benefited from its position on an important first major excavation at Bhaja, the caves appear maritime trading point connecting the parts of to have a rather irregular structure as a result of western India with the cities in the interiors and poor planning and numerous after-thoughts with became a stopping place for itinerant pilgrims, very simple architectural elements. However, monks and merchants. Beside a Brahmanical caves year by year after gaining initial experiences the at Udayagiri near Vidisha in neighbouring Madhya excavators incorporated more complex and up Pradesh, cut a little over fifty years earlier, no other to date forms. They introduced now peristyles to sites were excavated in whole of western Deccan Vih ra, introduced beautiful ornamental pillars for about three hundred years. Architects and and sculptures were lavishly decorated. worksmen employed at Bhaja had to re-discover The caves of Bhaja also represent the the technique of rock cutting that has been partly very first example in Western India where earthen lost to living memory. plaster technology was practiced for decorative As a consequence, the artists were totally purposes. The techniques and composition of the unfamiliar with the procedures needed to both earthen plaster were subsequently improved in the *Researcher, Deccan College Post Graduate and Research Institute, Pune-411 006, India. Email:[email protected] **Archaeological Survey of India, Science Branch, Fort St. George, Chennai - 600 009, India ***Archaeological Survey of India, Science Branch, Bibi-Ka-Maqbara, Aurangabad - 431 004, India 432 INDIAN JOURNAL OF HistorY OF SCIENCE later caves in the form of selection of better soil facades. As result, the sun rays directly fall to the type, addition of ingredients etc in the earthen mix. caves in the afternoon. The caves of Bhaja played However, it is interesting to explore the earliest an important role as maritime trading centre earthen plaster technology prepared for application besides preaching of Buddhism in the area during on walls and ceilings at Bhaja caves representing the period of 100 B C to 300 A D. the first major excavation of Buddhist legend in Western India. It is reported that though Bhaja caves were excavated in 1st Century B C, earthen plastering was accomplished in 2nd century A D (Dhavalikar, 1984). Irrespective of time, Bhaja represents first major example of earthen plaster technology in India. The investigation of the composition and characteristics of Bhaja caves earthen plaster will, therefore not only throw light on the development of technology at the initial stage, but also some glimpse about understanding and knowledge of ancient Indians in the field. The Bhaja caves is situated at a distance of about 50 km to the north of famous city of Pune adjacent to Pune – Mumbai Highway (Fig.1). The caves been excavated at a steep Fig. 2. Plan of Bhaja caves The present research is inspired by the revival of traditional ancient earthen plaster technology needed for its restoration showing losses and damage to various extents during course of time. The ancient technicians all over the world mainly relied on multi layer system of plastering which considerably enhance resistance of external layer to rain water penetration besides preventing accumulation of moisture within the plaster masonry. This plastering technique also Fig.1. The location map showing the Bhaja caves. facilitated quick evaporation of moisture from within the masonry. The earthen plasters in ancient gradient of rugged Sahayadri hills of Deccan on structures have exhibited excellent durability and coastal belt of Western India in densely forested were widely used throughout the centuries for area and during monsoon heavy rains lashes decorative coatings for ceiling and walls of both the entire coastal belt. The plan of Bhaja caves exterior and interior finish. is shown in Fig.2. The Bhaja caves are facing towards west and many of the caves did not have MUD PLASTER WALL PAINTINGS OF BHAJA Caves: COMPOSITION AND PERFORMANCE 433 In case of mural artworks, the conservation subsequent detachment. The earthen plaster begins problems can directly be linked to the earthen to absorb moisture at 67 % relative humidity which plaster support in structural building. The causes loss of mechanical strength, degradation knowledge of traditional earthen plaster preparation of the binder and loss of painted layer due to lose is also vital in case of both restorations and repair adhesion with the background. In-situ climatic interventions of ancient cultural heritage. However, condition and application of any surface coatings technological complexity due to composition of over the paint layer will be further detrimental several layers with different micro-structures to decorative art due to differential dimensional and their role in regulating moisture movement changes, shrinkage and swelling of support layers towards external surfaces makes investiation and difference in water vapour permeability. Any about earthen plaster a little complex. The preservative coating over murals will inhibit water characteristic and nature of raw materials, their vapour transmission through various substrate selection criteria as well as relative properties of layers as paintings on earthen support is highly various components were considerat to understand water sensitive. When active deterioration is technological development of the period for observed, restoration without understanding compatible and correct intervention. Many of the causes and mechanism of deterioration may cause recipes of ancient earthen plaster are still unknown more damage in the long run (Cathers, 1999). All and often co-related to the availability of local factors of deterioration affect the original fabric resource materials and knowledge and experience and therefore proper understanding about original of artisans. From restoration point of view, earthen earthen plaster layers, clay fabric and deterioration plaster characterization is the first necessary step to process is essential. design a suitable plaster mix taking into account the Earth, a highly heterogeneous material compatibility that must exist between the original were used in the construction of shelters for and new material. For that reason, only analytical mankind for thousands of years (Mellaart, 1964). characterization of earthen plaster can provide Traditionally, the mud plaster is prepared by data for planning conservation strategies. In India, exploiting soil mainly composed of sand, silt the characterization of ancient earthen plaster in and clay with straw added to prevent excessive diverse geological regions of the country is still cracking during drying. For earthen support to in primitive stage (Singh, 2015; Singh, 2014). function well, an equitable distribution of sand, Conservation of decorated surfaces on earthen silt and clay is desirable. Too much silt is not a plaster support layers constitutes a specialized good binder and provides material that is prone area within the field of heritage conservation. to damage by grain breakage on account of large Published research in this field is quite limited grain size and very less contact cohesion. The due to complexity of diverse materials in different non-clays are of grain size greater than clay (< 2 support layers and availability of sufficient µm) and are divided into the grain categories of silt samples for analytical purpose (Warron,1999; (2 – 50 µm) and sand (50 µm – 2 mm) in diameter. Artioli, 2008, and Singh 2013). Research cannot Due to small surface areas, non